Circle grid analyses and forming limit diagrams can be used to determine forming severity of a sheet metal stamping at some point in its production history. The technique, however, is not amenable to routine monitoring of the forming system over months and years of production. This function is best performed using statistical techniques, such as statistical process quality control.
Statistical deformation control, or SDC, merges these separate techniques into a single method to both analyze and monitor either the entire forming system or any of its components.
A control chart of final stamping deformation permits dynamic monitoring of the forming system. A key element in the successful application of SDC is the rapid, press-line measurement of deformation by a nondestructive, ultrasonic thickness gauge. The control chart shows the stability of the forming system and is capable of providing early warning of impending process failures.
Additional levels of analysis are possible with SDC. First, a feature unique to SDC for formability analysis is that each control chart can be subdivided and calibrated according to forming severity. Second, material variability can be separated from process variability through the use of a reference steel. Third, the sensitivity of the forming system to individual inputs can be determined.
The details of the SDC technique and its application are defined in this paper. A press shop experiment with SDC is used to illustrate the concept.